Salt-templated synthesis of defect-rich MoN nanosheets for boosted hydrogen evolution reaction

Abstract

Two-dimensional defect-rich molybdenum nitride (dr-MoN) nanosheets were successfully prepared via a NaCl template-directed synthesis route followed by an incomplete ammoniation of MoO₃ nanosheets. With additional edge defects arising from the etched MoO₃ compared to those in the intact MoN nanosheets, dr-MoN was capable of efficiently electro-catalyzing the hydrogen evolution reaction (HER) under both acidic and alkaline conditions with impressive activity and durability. The dr-MoN-0 catalyst possessed an ultra-small onset overpotential of approximately 10 mV in 0.5 M H₂SO₄ electrolyte, which is competitive with that of the Pt/C catalyst. Overpotentials of only 125 mV and 139 mV are required to deliver a current density of 10 mA cm⁻² for the dr-MoN-0 catalyst in 0.5 M H₂SO₄ and 1 M KOH, respectively. More importantly, the dr-MoN-0 maintained a prominent amperometric (I–t) durability during a 20 h test and also a superior cycling stability with negligible overpotential loss, all of which are among the best results for current MoN based HER catalysts. The exceptional performance was attributed to the defect-abundant structure which resulted in the formation of tiny cracks on the surface of the nanosheets and caused the additional exposure of active edge sites. These findings highlight the prospective potential of dr-MoN with additional active edge sites as highly efficient and stable platinum-free electrocatalysts towards the HER.